Self-Organization of Polystyrene-b-polyacrylic Acid (PS-b-PAA) Monolayer at the Air/Water Interface: A Process Driven by the Release of the Solvent Spreading

On the Preparation of Thin Films of Stearyl Methacrylate Directly Photo-polymerized at the Air-Water Interface

Characterization of bidimensional polymeric films at the air-water interface in the Langmuir trough, despite being a recurrent topic, usually refers to films of already formed polymeric materials, with very scarce reports on direct polymerization at the air-water interface. In the present work, we studied the photo-polymerization of stearyl methacrylate directly at the air-water interface under a nitrogen atmosphere, with the radical initiator solubilized in the aqueous phase. Two-dimensional (2D) polymerization was monitored by measuring the pressure-area isotherm at different irradiation times. The polymerization leads to a film with an isotherm different from that observed for the monomer, where the surface pressure is directly related to the irradiation time. The shape of this isotherm confirms the presence of a compressed liquid phase, where a higher order can be attained as a consequence of stronger packing forces involving polymer chains. The presence of inter-chain interactions allows rearrangements on the surface of the subphase, and even before the collapse a dense 2D ordering (with a solid phase-like behavior) can be observed. We present a new one-step, solvent-free procedure to obtain a photo-polymeric film directly at the air-water interface, which can be transferred to a solid surface by the Langmuir-Blodgett method, allowing film preparation of controlled thickness. Films were characterized by measuring properties such as thickness, roughness, and hydrophobicity and comparing them with films obtained from a conventional polymer. We report the differences between the interfacial behavior of amphiphilic molecules and nanomaterials such as films obtained by photo-polymerization, PSMA, directly on the air-water interface.

Weak Polyelectrolytes as Nanoarchitectonic Design Tools for Functional Materials: A Review of Recent Achievements

The ionization degree, charge density, and conformation of weak polyelectrolytes can be adjusted through adjusting the pH and ionic strength stimuli. Such polymers thus offer a range of reversible interactions, including electrostatic complexation, H-bonding, and hydrophobic interactions, which position weak polyelectrolytes as key nano-units for the design of dynamic systems with precise structures, compositions, and responses to stimuli. The purpose of this review article is to discuss recent examples of nanoarchitectonic systems and applications that use weak polyelectrolytes as smart components. Surface platforms (electrodeposited films, brushes), multilayers (coatings and capsules), processed polyelectrolyte complexes (gels and membranes), and pharmaceutical vectors from both synthetic or natural-type weak polyelectrolytes are discussed. Finally, the increasing significance of block copolymers with weak polyion blocks is discussed with respect to the design of nanovectors by micellization and film/membrane nanopatterning via phase separation.

Surface Pressure-Induced Interdiffused Structure Evidenced by Neutron Reflectometry in Cellulose Acetate/Polybutadiene Langmuir Films

Binary blends of water-insoluble polymers are a versatile strategy to obtain nanostructured films at the air-water interface. However, there are few reported structural studies of such systems in the literature. Depending on the compatibility of the polymers and the role of the air-water interface, one can expect various morphologies. In that context, we probed Langmuir monolayers of cellulose acetate (CA), of deuterated and postoxidized polybutadiene (PBd) and three mixtures of CA/PBd at various concentrations by coupling surface pressure-area isotherms, Brewster angle microscopy (BAM), and neutron reflectometry at the air-water interface to determine their thermodynamic and structural properties. The homogeneity of the films in the vertical direction, averaged laterally over the spatial coherence length of the neutron beam (∼5 μm), was assessed by neutron reflectometry measurements using D₂O/H₂O subphases contrast-matched to the mixed films. At 5 mN/m, the whole mixed films can be described by a single slightly hydrated thin layer. However, at 15 mN/m, the fit of the reflectivity curves requires a two-layer model consisting of a CA/PBd blend layer in contact with the water, interdiffused with a PBd layer at the interface with air. At intermediate surface pressure (10 mN/m), the determined structure was between those obtained at 5 and 15 mN/m depending on film composition. This PBd enrichment at the air-film interface at high surface pressure, which leads to the PBd depletion in the blend monolayer at the water surface, is attributed to the hydrophobic character of this polymer compared with the predominantly hydrophilic CA.

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research

This article aims to provide an overview of broad range of applications of synchrotron scattering methods in the investigation of nanoscale materials. These scattering techniques allow the elucidation of the structure and dynamics of nanomaterials from sub-nm to micron size scales and down to sub-millisecond time ranges both in bulk and at interfaces. A major advantage of scattering methods is that they provide the ensemble averaged information under in situ and operando conditions. As a result, they are complementary to various imaging techniques which reveal more local information. Scattering methods are particularly suitable for probing buried structures that are difficult to image. Although, many qualitative features can be directly extracted from scattering data, derivation of detailed structural and dynamical information requires quantitative modeling. The fourth-generation synchrotron sources open new possibilities for investigating these complex systems by exploiting the enhanced brightness and coherence properties of X-rays.

Supramolecular organization and optical properties of BODIPY derivatives in Langmuir–Schaefer films

Formation of thin-film nanomaterials, promising for nanoelectronic applications, with a given structure based on four new BODIPY dyes.

Self-organization of octa-phenyl-2,3-naphthalocyaninato zinc floating layers

Formation of thin-film nanomaterials, promising for nanoelectronic applications, with a given structure based on octa-phenyl-2,3-naphthalocyaninato zinc.

Structural hierarchy in blends of amphiphilic block copolymers self-assembled at the air-water interface

We present a concurrent self-assembly strategy for patterning hierarchical polymeric surface features by depositing variable-composition blends of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and polybutadiene-block-poly(ethylene oxide) (PB-b-PEO) block copolymers at the air-water interface. Hierarchical strand networks of hydrophobic PS/PB blocks anchored via PEO blocks to the water surface, with an internal phase-separation structure consisting of periodic domains of PS blocks surrounded and connected by a matrix of PB blocks, are generated by the interplay of interfacial amphiphilic block copolymer aggregation and polymer/polymer phase separation. In contrast to the cylinder-in-strand structures previously formed by our group in which interfacial microphase separation between PS and PB blocks was constrained by chemical connectivity between the blocks, in the current system phase separation between PS and PB is not constrained by chemical connectivity and yet is confined laterally within surface features at the air-water interface. Investigations of multi-component polymer systems with different connectivities constraining repulsive and attractive interactions provides routes to new hierarchical surface patterns for a variety of applications, including photolithography masks, display technology, surface-guided cell growth and tissue engineering.

Coupled Effects of Spreading Solvent Molecules and Electrostatic Repulsions on the Behavior of PS-b-PAA Monolayers at the Air-Water Interface

We describe the surface behavior of PS-b-PAA monolayers at the air/water interface using N,N-dimethyformamide (DMF) as spreading solvent. At low pH, when the PAA blocks are neutral, the surface pressure versus molecular area isotherm shows a pseudoplateau associated with the presence of remaining spreading solvent molecules in the monolayer, as we described in a former study (Guennouni et al., Langmuir, 2016). We show here that the width of the plateau decreases when increasing pH up to its complete disappearance at high pH, when PAA blocks are fully charged, although two regimes of compressibilities on the isotherm still exist. A refined structural study at pH 9 combining specular neutron reflectivity (SNR), grazing-incidence small-angle X-ray scattering (GISAXS), and atomic force microscopy (AFM) in liquid measurements shows that (i) PAA blocks are stretched in solution, as expected from polyelectrolyte brushes in the osmotic regime; (ii) the system undergoes a spinodal decomposition during deposit at the air/water interface in the presence of DMF. Upon compression, the Q_xy* position of the peak associated with the spinodal structure remains almost constant but its intensity evolves strongly and passes through a maximum at intermediate pressures. This reveals two operating processes in the system: strong electrostatic repulsions between chains that prevent in-plane reorganizations and force such reorganizations to occur from the surface to the volume and progressive expulsion of the DMF molecules from the monolayer. These processes have antagonist effects on the intensity of the peak: the increase of the repulsions makes it more pronounced, whereas the expulsion of solvent makes it vanish due to the loss of contrast.

Enhanced acaricidal activity of ricinine achieved by the construction of nano-formulation using amphiphilic block copolymer

Amphiphilic block copolymer PEO–PCL improves the encapsulation of ricinine and enhances the acaricidal efficiency of the pesticide on V. unguiculata (L.) when compared to the formulations made by surfactants.